Molded thermoplastic and thermoset articles, such as those made from polyolefins, polycarbonate, polyester, polyethylene, polypropylene, polystyrene and polyurethanes, are utilized in numerous applications including those for the automotive, marine, recreation, construction, office products, and outdoor equipment industries. For example, automotive industry applications include body panels, wheel covers, bumpers, head and tail lamps, fenders, hoods, and dashboards.
Use of the molded articles is not without problem, as the surface quality may not meet required standards, such as durability, chemical resistance, and weather resistance. In many instances, the molded thermoplastic articles may need to be coated to satisfy the above-noted requirements or to facilitate paint adhesion.
Countless methods have been developed to apply various coatings to the molded articles to improve the surface characteristics thereof.
Previously, molded work pieces were formed in a mold, the molded product removed, and a coating was then applied on the surface of the molded work piece by a coating process, such as a surface treatment, primer coating, top coating, painting, etc. Hence the foregoing methods required an additional step to achieve a finished surface on a work piece, i.e. treating the surface of the pre-formed work piece prior to applying a paint or coating. These methods required additional steps and increased costs of preparing the molded work piece surface.
It became desirable, therefore, to have a method by which a coating could be applied to a work piece in the mold, resulting in a coated work piece the surface of which would be finished and suitable for use as is in an end use application, or which would require less or no surface preparation treatment than heretofore utilized.
The application of in-mold coatings (IMC) to thermoplastic or thermoset materials to provide generally smooth surfaces, improve durability and other surface properties, and to reduce or eliminate substrate porosity is known. A number of in-mold coating methods have been employed for applying coatings, in compression molding methods or injection molding methods employing molding materials of thermosetting resins, such as SMC (sheet molding compound) and BMC (bulk molding compound) (e.g., U.S. Pat. Nos. 4,076,788; 4,081,578; 4,331,735; 4,366,109; and 4,668,460).
Heretofore, the in-mold coatings which have been applied to molded articles typically covered the entire surface of the article. The coverage of the coating was controlled by only the amount of coating applied, such as in the case of an undershot, or possibly the physical boundaries of the mold cavity.
Often, an in-mold coating is applied to the same side of a molded article from which the substrate material was injected. The injected in-mold coating will seek the path of least resistance and thus flow into generally any orifice or opening, including the substrate injection orifice. Accordingly, the in-mold coating can flow into the gate pin of an injection device and infiltrate the same, contaminating the substrate resin therein. It would therefore be desirable to provide a barrier to prevent an in-mold coating from accessing a substrate injection orifice such as a gate pin assembly. The present invention device or structure may also be used in a mold which has an insulated runner, hot runner or the type of runner normally referred to as a sprue.